1. Field of the Invention
The present invention relates to a steering apparatus which has a tilt-and-telescopic adjustment mechanism and which is capable of preventing shape distortion of a bearing from an inner column due to tightening during tilt-and-telescopic adjustment and securing both telescopic travel of the inner column and tightening retention.
2. Description of the Related Art
In recent years, many so-called short column-type steering apparatuses with shorter axial distances from a steering shaft to an upper universal joint have become available. With such a short column-type steering apparatus, an outer column has a shorter length in an axial direction and an upper universal joint moves together with an inner column in an axial direction during telescopic adjustment. Related art Japanese Patent Application Laid-open No. 2005-335491 discloses a short column-type steering apparatus having a tightening structure with high stiffness. An outer diameter section of an inner column 1 is configured such that an outer diameter of the outer diameter section decreases in stages from front to rear of a vehicle body to form an large outer diameter section 16A, a medium outer diameter section 16B, and a small outer diameter section 16C (refer to FIG. 6 of Japanese Patent Application Laid-open No. 2005-335491).
An inner diameter of the large outer diameter section 16A of the inner column 1 is formed in a dimension that enables the large outer diameter section 16A to enclose, but not interfere with, an upper universal joint 71. An inner diameter section of an outer column 3 is configured such that an inner diameter of the inner diameter section decreases in stages from the front to the rear of the vehicle body to form an large inner diameter hole 33A and a medium inner diameter hole 33B (refer to FIG. 7 of Japanese Patent Application Laid-open No. 2005-335491). The large outer diameter section 16A of the inner column 1 is guided by the large inner diameter hole 33A and the medium outer diameter section 16B of the inner column 1 is guided by the medium inner diameter hole 33B and, accordingly, the cylindrical inner column 1 is supported so as to be telescopically movable in an axial direction of the outer column 3.
At a maximum telescopic position (refer to reference numeral (1) in FIG. 9 of Japanese Patent Application Laid-open No. 2005-335491) to which the inner column 1 has been pulled out by a maximum distance toward a driver and a middle telescopic position (refer to reference numeral (2) in FIG. 9 of Japanese Patent Application Laid-open No. 2005-335491), the upper universal joint 71 penetrates into the outer column 3. Therefore, even with a short column having a shorter distance to the upper universal joint 71, a long telescopic stroke of the inner column 1 can be secured. At this point, since the large outer diameter section 16A that encloses the upper universal joint 71 is guided by the large inner diameter hole 33A, a guide length S1 at the maximum telescopic position and a guide length S2 at the middle telescopic position are secured.
In a vicinity of a minimum telescopic position (refer to reference numeral (3) in FIG. 9 of Japanese Patent Application Laid-open No. 2005-335491) to which the inner column 1 has been pushed in by a maximum distance toward the front of the vehicle body, the large outer diameter section 16A that encloses the upper universal joint 71 detaches from the large inner diameter hole 33A of the outer column 3 and only the medium outer diameter section 16B is guided by the medium inner diameter hole 33B of the outer column 3. Therefore, a guide length S3 of the inner column 1 at the minimum telescopic position is a minimum guide length.
Furthermore, a protrusion 15 is integrally formed above the large outer diameter section 16A of the inner column 1 (refer to FIG. 8 of Japanese Patent Application Laid-open No. 2005-335491), and a guide groove 34 that guides the protrusion 15 is formed on the outer column 3 over an entire length of the telescopic stroke of the inner column 1 (refer to FIG. 5 of Japanese Patent Application Laid-open No. 2005-335491). Due to the protrusion 15 and the guide groove 34 abutting each other at the minimum telescopic position, a guide length S4 of the inner column 1 is extended and transverse slip due to a gap at a fitting section is resolved (refer to FIG. 7 of Japanese Patent Application Laid-open No. 2005-335491).
However, Japanese Patent Application Laid-open No. 2005-335491 entails the following problems. First, an upper steering shaft 6 is rotatably supported by an upper bearing 11 and a lower bearing 12 in the inner diameter section 13 of the inner column 1. The lower bearing 12 is arranged on an inner circumference of the medium outer diameter section 16B, and when the medium outer diameter section 16B is pressed by the outer column 3 during clamping, the lower bearing 12 may become distorted. Distortion of the lower bearing 12 destabilizes the rotatable support of the steering shaft 6. Such a phenomenon will now be described with reference to a schematic view (FIG. 6). Moreover, only for FIG. 6 which illustrates related art, reference numerals will be parenthesized in order to distinguish FIG. 6 from the present invention.
When the outer column 3 is tightened, a pressing force F causes an outer diameter d1 of the inner column 1 to contract by a minute dimension Δd1 and the inner column 1 deforms elliptically. As a result, the outer diameter changes to d1−Δd1 (refer to FIG. 6A). The effect of the deformation of the inner column 1 extends to the lower bearing 12 via the inner column 1. Consequently, an outer wheel of the lower bearing 12 is pressed and deforms elliptically, and the lower bearing 12 becomes no longer capable of providing rotational movement in a smooth manner (refer to FIG. 6B).
In addition, the large outer diameter section 16A that encloses the upper universal joint 71 of the inner column 1 is structured so as to move in an axial direction inside the large inner diameter hole 33A of the outer column 3. Therefore, extending the length of the large inner diameter hole 33A in order to secure telescopic stroke within the limited length of the outer column 3 in the axial direction results in shortening a length of the medium inner diameter hole 33B of the outer column 3 which embraces and fixes the inner column 1, and destabilizes clamp retention. Conversely, extending the length of the medium inner diameter hole 33B in order to increase clamp retention shortens the length of the large inner diameter hole 33A and prevents a long telescopic stroke from being obtained.
Furthermore, since the large outer diameter section 16A that encloses the upper universal joint 71 of the inner column 1 and the large inner diameter hole 33A of the outer column 3, and the medium outer diameter section 16B of the inner column 1 and the medium inner diameter hole 33B of the outer column 3, are respectively formed so as to correspond to each other, dimension management is difficult. If dimensions of the large outer diameter section 16A and the large inner diameter hole 33A do not correspond to each other, telescopic travel cannot be performed in a smooth manner. On the other hand, if dimensions of the medium outer diameter section 16B and the medium inner diameter hole 33B do not correspond to each other, clamp retention becomes unstable. As described above, the formation of two different outer diameters and inner diameters on the inner column 1 and the outer column 3 makes dimension management difficult and increases cost.